Many ion-generating devices that utilize a discharge phenomenon have been put into practical use. Each of these ion-generating devices is generally configured with an ion-generating element for generating ions, a high-voltage transformer for supplying a high voltage to the ion-generating element, a high-voltage transformer drive circuit for driving the high-voltage transformer, and a power supply input portion such as a connector.
Ion-generating elements are roughly categorized into two major types. One type uses a metal wire, a metal plate having an acute-angled portion, needle-shape metal, or others as a discharge electrode, and uses a metal plate, a grid, or others at a ground potential as a counter electrode, or uses the ground as a counter electrode without specially disposing a counter electrode. In this ion-generating element, air serves as an insulator. This ion-generating element utilizes a scheme to produce a discharge phenomenon by causing electric field concentration at a tip of an electrode, identified as an acute-angled portion, when applying a high voltage to the electrode, and causing an electrical breakdown of the air in close vicinity of the tip.
The other type is configured with a pair of an induction electrode embedded in a high-breakdown voltage dielectric, and a discharge electrode disposed at a surface of the dielectric. The ion-generating element of this type utilizes a scheme to produce a discharge phenomenon by causing electric field concentration in proximity to an outer edge portion of the discharge electrode at the surface when applying a high voltage to the electrode, and causing an electrical breakdown of the air in close vicinity thereof.
As a high-voltage transformer that applies a high voltage to the above-described ion-generating element, a winding transformer having a primary winding and a secondary winding, and a piezoelectric transformer made of a piezoelectric ceramic element and utilizing a piezoelectric phenomenon, have been put into practical use.
As to the conventional ion-generating device, Japanese Patent Laying-Open No. 2002-374670, for example, describes an example. This ion-generating device is of a type in which an ion-generating electrode is set as a discharge electrode and no counter electrode is disposed. In this ion-generating device a piezoelectric transformer that supplies a high voltage to the ion-generating electrode, and a drive circuit for driving the piezoelectric transformer are mounted in a casing, and integrated by molding. It is noted that the ion-generating electrode is disposed outside the casing, and connected to a cable led out from the casing.
As to the high-voltage transformer, the above-described publication describes the differences between a piezoelectric transformer and a winding transformer, and their advantages and disadvantages, stating that although a piezoelectric transformer itself can be made more compact than a winding transformer, its peripheral circuitry becomes more complicated. This publication also describes that the high-voltage transformer and other components are mounted on the same substrate, and that the substrate is disposed in an outer casing by being lifted off from a bottom surface of the casing at a certain distance.
Patent Document 1: Japanese Patent Laying-Open No. 2002-374670